Gephi is an interactive visualization and exploration platform for all kinds of networks and complex systems, dynamic and hierarchical graphs. Runs on Windows, Linux and Mac OS X. Gephi is open-source and free.
Agna is a freeware application designed for social network analysis, sociometry and sequential analysis. Platform-independent, friendly and easy-to-learn, integrated visual network editor, html output, free.
The Rasterbator creates huge, rasterized images from any picture. Upload an image, print the resulting multi-page pdf file and assemble the pages into extremely cool looking poster up to 20 meters in size.